Protective coatings for medical devices

ABSTRACT

This invention relates to a method of providing a coating on a medical device, especially a dilatation balloon, which improves the durability of the balloon.

FIELD OF THE INVENTION

This invention relates to a method of providing a coating on a medicaldevice, especially a dilatation balloon, which improves the durabilityof the device.

BACKGROUND OF THE INVENTION

Catheter devices having an inflatable balloon mounted at the distal endare useful in a variety of medical procedures such as coronaryangioplasty, stent delivery and placement for the opening of occluded orblocked blood vessels, for urological and reproductive surgeries, and todeliver biologically compatible fluids, such as radiologically opaquefluid for contrast x-rays to precise locations within the body. Theseprocedures often involve the insertion of the device into blood vesselsof extremely reduced diameter for long distances through the vascularsystem. These applications require thin walled high strength balloons ofa relatively inelastic or non-compliant nature that have predictableinflation properties.

Once the balloon is positioned at the desired location, it is inflatedby supplying liquid under pressure through an inflation lumen to theballoon. The inflation of the balloon causes stretching of a bloodvessel, for instance, to reestablish acceptable blood flow through theblood vessel.

Balloon catheters are therefore produced from materials that canwithstand high pressure, even at very low film thicknesses. The strengthof the material is determined by measuring the tensile strength, andfilms with high strength relative to film thickness are chosen. Examplesof materials useful in balloon catheters includepolyethyleneterephthalate (PET); polyether-polyester block copolymerssuch as the Hytrel® series of block copolymers, also referred to asthermoplastic polyester elastomers, available from Du Pont inWilmington, Del. or the Arnitel® series available from DSM, theNetherlands, such as Arnitel® 540; and polyamide/polyether/polyesterssuch as PEBAX® 6333, 7033 and 7233. However, films produced from suchmaterials tend to be harder, and to be scratch and puncture sensitive.

Scratches, abrasions, and even punctures can occur during handling andstorage of the devices, or during use. Stents or other objects mayscratch or puncture the balloon. Friction between the device and thevessel through which it is being passed can result in failure of theballoon at the weakened points that result from scratches, abrasions orpunctures. Lubricious coatings can reduce the friction between thedevice and the vessel wall, but provides only limited protection anddoes not really address the problem of scratches, abrasions andpunctures. These coatings improve the success rate by altering thecoefficient of friction between the device and the vessel wall, but donot address the scratch and puncture resistance other than by buildingfilm thickness.

Balloon failure at points of abrasions, scratches or punctures can be aproblem during inflation. The balloon may prematurely burst, or thepoint at which the abrasion, scratch or puncture is located tends to beweaker, and when inflated, will have a tendency to over expand at thatpoint, leading to over extension or bulging in the balloon wall at theweakened point. These bulges can in turn cause damage to blood vessels,for instance. Over inflation is also a problem during stent delivery.

More compliant materials tend to be more scratch and puncture resistant,but do not provide the strength required to withstand the pressures usedin some of these procedures. Non-compliance which is the ability toresist expansion beyond a predetermined size upon pressure, and tosubstantially maintain a profile, is required for balloon catheters,especially those utilized in small vessels. Excessive expansion of morecompliant materials can result in the rupture or dissection of bloodvessels.

There is a continuing need in the medical device area to provideimproved protective layers or coatings to balloons formed ofnoncompliant materials to increase the resistance of such balloons toscratches, abrasions and punctures. These improved coatings provideincreased resistance by building film thickness, but they do not addressthe issue of what occurs in the event that the balloon is scratched,abraded or punctured.

Efforts have been made to coat a balloon with a continuous coating of athin durable material. The problem associated with such continuouscoatings in that if a pinhole is present in the underlying balloonmaterial, as the balloon is inflated, the coating will also inflate, andat the point of the pinhole, can separate from the balloon material andform a bubble which can dissect an artery or vessel.

Specific examples of such problems occur with oriented PET which iscommonly used for forming catheter balloons by a stretch blow moldingmethod. The PET can exhibit pinholes that emit a high-velocity jet ofinflation fluid during inflation. This then will result in the bulgeforming in the outer coating layer which can cause artery dissection.Pet also exhibits low tear resistance and does not take a crease.

One such method of improving the scratch or abrasion resistance ofmedical apparatuses is found in U.S. Pat. No. 5,766,158 issued Jun. 16,1998 to Opolski which describes a protective surface coating for amedical device which contains a matrix polymer and a reinforcing agentto decrease the sensitivity of the medical apparatus to injuries, suchas scratches, punctures, and the like. The reinforcing agent islamellar, platelet, or fiber-like in structure and has a higher surfacehardness that the surface hardness of the medical apparatus.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a protective coatingwhich improves the durability of a medical device, especially adilatation balloon, and also addresses the problems which can arise if ascratch, abrasion or puncture occurs in, for instance, a balloon wall.The coating is noncontinuous in nature, thus preventing bubbling oraneurysms in the outer protective coating if the underlying device, i.e.balloon wall, becomes damaged and allows inflation medium to escape.

The present invention further relates to a method of providing adilatation balloon with improved durability comprising the steps offorming a balloon and applying a noncontinuous protective coating tosaid balloon. The coating comprises a polymeric material which gives theballoon improved durability.

The pattern of the coating may be a “waffle” pattern, a “strip” pattern,or a pattern having circular perforations, or any other pattern of adiscontinuous nature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a standard dilatation balloon in anuncoated condition.

FIG. 2 is a perspective view of a standard dilatation balloon with a“waffle” pattern coating of the present invention.

FIG. 3 is a perspective view of a standard dilatation balloon with a“stripe” pattern coating of the present invention.

FIG. 4 is a perspective view of a standard dilatation balloon with asubstantially solid coating having a uniform pattern of circularperforations.

FIG. 5 is a perspective view of a standard dilatation balloon havinganother embodiment of a “stripe” pattern coating and in an uninflatedstate.

FIG. 6 illustrates the same balloon as shown in FIG. 5 but now havingpressure applied as during inflation. No aneurysm is exhibited.

FIG. 7 illustrates a balloon having a continuous coating of polyurethanepolymer in its inflated state. An aneurysm is formed in the coating.

DETAIL DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

The present coating may be utilized on any medical device which can bedamaged by scratching, abrasions, and/or punctures, especially catheterdevices, and in particular, balloon catheters or dilatation balloons.

A dilatation balloon of the present invention is illustrated generallyat 10 in FIG. 1, and includes an inflatable balloon 14 mounted at thedistal end of an elongated flexible shaft 12. Balloon 14 has a balloonwall 13; Except as noted herein, catheter 10 is conventional in itsconstruction, providing a lumen communicating with the interior of theballoon 14, for inflation and deflation of the balloon, and otheroptional features conventional in the dilatation catheter art. Theballoon 10, has an inflated configuration, illustrated in FIG. 1 and ismade up of three main portions: the body 14, the cones 26 and the waistportions 28. Balloon catheters of this type are described in U.S. Pat.No. 5,490,839 to Wang et al. issued Feb. 13, 1996 and hereinincorporated by reference.

FIG. 2 illustrates the same balloon 14 coated with a “waffle” patterncoating 15 of the present invention coated over balloon wall 13.

FIG. 3 illustrates the same balloon construction with another embodimentof the coating 16 of the present invention having a different patternthan that exhibited in FIG. 2. The pattern in this diagram is a “stripe”pattern wherein the stripes run diagonally around the circumference ofthe balloon.

FIG. 4 illustrates the same balloon construction as in FIGS. 2 and 3with yet another embodiment of a the coating 17 of the present inventionhaving yet a different pattern than exhibited in the other figures. Thisembodiment illustrates a more solid coating which has circularperforations spaced at a uniform distance from one another. The size ofthe perforations may be varied.

FIG. 5 illustrates a balloon 20 in its uninflated state, and having a“stripe” pattern coating 18 of a polyurethane polymer, also referred toas a “shape memory polymer.” This pattern of has the stripes runninglongitudinally with the balloon whereas the pattern illustrated in FIG.3 exhibits stripes running diagonally around the circumference of theballoon 20. The polyurethane polymer utilized in this embodiment isavailable from Mitsubishi Heavy Industries, Ltd in Tokyo, Japan, underthe tradename of SMP-3510. The balloon 20 has an inner wire lumen 30 fordelivery of the inflation media. The balloon exhibits a pinhole 50 leftof center and beneath a coated section of the balloon.

FIG. 6 illustrates the same balloon 20 as shown in FIG. 5 duringinflation. Inflation medium can be seen venting from out the edges ofthe coated section. Desirably, no aneurysm is formed in the coatingbecause the inflation medium can easily escape. The inflation media 55is exiting through the pinhose 50 and can be seen venting out the sidesof the discontinuous stripe coating 18 on balloon 20. The large invertedwater droplet 60 seen in the center from of the photograph is forming asa result of the inflation media 55 flowing out of the pinhole 50. Boththe stream of inflation media 55 and the droplet 60 are on the same sideof the balloon 20. Such droplet formation would not be exhibited werethe balloon in an aqueous environment such as a vessel of a patient butsuch fluid would be carried away in the blood.

FIG. 7 illustrates a balloon 20 having a continuous coating 19 ofpolyurethane polymer, SMP-3510, available from Mistubishi HeavyIndustries, Ltd, in its inflated state. An aneurysm 40 is formed in thecoating. Inner wire lumen 30 is for inflation media delivery.

While these are some suggestions as to types of patterns that may beused in the coating method, there are a limitless variety of patternsand sizes of patterns that may be utilized to achieve the objectives ofthe present invention. Any pattern wherein there is discontinuity in thecoating, may alleviate the formation of pinholes which may ultimatelylead to aneurysms in the balloon construction, and to damage to thepatients vessels.

The balloons may be constructed of thermoplastic polymeric materialsincluding thermoplastic elastomers, i.e. block copolymers; copolymersand terpolymers of ethylene; homopolymers, copolymers and terpolymers ofpropylene; ethylene α-olefins; polyesters; polyamides; polyurethanes;polycarbonates, vinyl copolymers; ionomer materials and so forth. Morespecifically, materials such as nylon, Selar®, polyether-polyester blockcopolymers (i.e. Hytrel® from DuPont or Arnitel® from DSM, Netherlands),Pebax® (polyether block amide copolymers), Surlyn®, polyethyleneterephthalate, polytetrafluoroethylene, polyvinyl chloride,polyetherurethanes, polyesterurethanes, polyurethane ureas, polyurethanesiloxane block copolymers, silicone polycarbonate copolymers, ethylenevinyl acetate copolymers, acrylonitrile-butadiene-styrene copolymers;polyphenylene sulfides; copolyesters or other similar extrudablethermoplastic, polymeric materials, or composites thereof may beutilized in the present invention. Thermosetting materials such aspolyimides may also be utilized.

The balloon wall may be noncompliant or compliant. Noncompliant balloonsare formed from relatively stiff materials includingpolyethyleneterephthalate (PET), high density polyethylene, polyamides,polycarbonates and stiff polyurethanes, and so forth. The balloon wallmay also be compliant and made of materials such as polyvinyl chloride,polyethylene, polyester copolymers, polyolefin copolymers and so forth.The present invention provides a particular advantage when the balloonwall is made of a stiff, noncompliant material. Such materials tend toscratch more easily, especially if a fold occurs in the balloon.

Some specific preferred balloon materials include polyether blockamides, such as Pebax® 7033 or 7233; polyester block ethers such asArnitel® EM 40; polyethylene terephthalate (0.64 to 0.8 IV PET); andnylon. The formation of catheter balloons made of block copolymerelastomers where the hard segments are polyester or polyamide and thesoft segments are polyether, is discussed in U.S. Pat. No. 5,556,383issued Sep. 17, 1996 to Wang et al. herein incorporated by reference.The formation of catheter balloons made of PET is discussed in U.S. Pat.No. 5,714,110 issued Feb. 3, 1998 to Wang et al. herein incorporated byreference. The formation of catheter balloons produced from blockcopolymer elastomers is discussed in U.S. Pat. No. 5,830,182 issued Nov.3, 1998 to Wang et al., herein incorporated by reference.

A typical method of balloon formation involves first extruding a tubularpreform, and subsequently blowing the tubular preform into a balloon.The balloon has what is referred to as a body, at least one coneportion, and at least one waist portion.

Suitable balloon forming techniques which may be employed are well knownin the art and may be carried out in any conventional manner withconventional extrusion and blowing techniques. Such techniques forballoon formation are discussed in U.S. Pat. No. 4,490,421 to Levy andin U.S. Pat. No. 5,348,538 issued Sep. 20, 1994 to Wang et al. hereinincorporated by reference.

The balloon has a coating over the balloon wall. Preferably, the coatingwill be on the balloon body. However, the cones and the waist portion(s)may also be coated. Any thermoplastic polymeric material which isdissolvable in solvent, and which improves the durability of the balloonmay be utilized. The coating polymer is desirably sufficiently flexibleand elastic at body temperature and has only a minor, if any, impact onthe compliance characteristics of the balloon. The coating materialpreferably does not adversely affect the compliance characteristics ofthe balloon itself. The polymeric coating may also preferably have somesurface tack for certain applications including stent deliverycatheters. A certain amount of tack may help hold the stent moresecurely when the stent is in the crimped down position.

The polymers may be thermoplastic or thermoset polymeric materials.Thermoplastic materials useful to the present invention include any typeof material from which the balloons themselves may be produced, as wellas many others. Examples of such materials include vinyl polymers,fluorinated and chlorinated polymers, polyolefins, polyurethanes,polystyrene, polyesters, nylons, polyamides, polycarbonates,polyacrylates, poly(meth)acrylates, copolymerized versions, and soforth. Rubbery block copolymers include those having the generalconfiguration of linear, radial, star, Y-block, multiblock and so forth.

More specifically, the coating material may include polyvinyl chloride;polyethylene terephthalate; polyethylene homopolymers;styrene-butadiene-styrene block copolymers;styrene-ethylene/butylene-styrene block copolymers;styrene-ethylene/propylene-styrene block copolymers;styrene-isoprene-styrene block copolymers; polyester elastomers,polyether-block amides; copolymers of ethylene and vinyl acetate,n-butyl acrylate, methylacrylate; interpolymers of ethylene and at leastone alpha-olefin; and so forth.

A preferred class of thermoplastic polymers useful for the coating arethe thermoplastic polyurethane polymers.

Thermosetting polymers have functional moieties which are capable ofcrosslinking with other functional moieties.

Thermosetting materials include polyurethanes formed from an isocyanateand a polyol; acrylics; acrylates; methacrylates; epoxies; unsaturatedpolyesters; silicones having hydrolyzable acetate groups; polysulfides;cyanoacrylates; formaldehydes condensed with urea, phenol, resorcinol,melamine for instance, and so forth. Thermosetting compositions refer tocrosslinkable compositions, even those that do not necessarily requireelevated temperatures to initiate the chemical reaction. It ispreferable to the present invention to initiate polymerization or cureusing electron beam or ultraviolet radiation.

In a preferred embodiment of the present invention, a polyurethanepolymer is utilized. The glass transition temperature of thesepolyurethane polymers may be adjusted by changing the molar ratio ofdiisocyanate, polyol and chain extender. Glass transition temperaturesmay also be varied by changing the polyol itself. An example of apolyurethane polymer is SMP-3510 available from Mitsubishi HeavyIndustries, Ltd. These polymers are also referred to as “shape memorypolymers.”

Water based polymers may also be utilized including polyurethanedispersions and emulsion polymers such as acrylics, vinyl acetatehomopolymers, vinyl acrylic copolymers, vinyl acetate ethylenecopolymers, and so forth. A preferable water base coating is a urethane.

The coating of the present invention is a noncontinuous coating and maybe referred to as a porous coating or pattern coating. Pattern coatingcan be achieved in a number of ways including roll coating, screenprinting, pad printing, spraying and so forth. In pad, roll or screenprinting, the coating application head, i.e. roll or pad, for instance,will have dimples or indentations which result in a noncontinuouscoating being applied to the balloon. The pattern is preferablysubstantially uniform.

A preferable coating pattern which may be obtained using a pad printingmethod may be referred to as a waffle pattern wherein the shape of theindentation may be any shape provided the repeating pattern issubstantially uniform. Typical indentation shapes are square or round.Such a pattern may be found in FIG. 2 or FIG. 3.

Spraying may also be employed to achieve a pattern type of coating tothe balloon but will result in a much less uniform noncontinuouscoating.

In the case of thermoplastic polymers, it will be preferable to firstdissolve the polymer in a solvent or a blend of solvents prior toapplying the coating to the balloon. Suitable solvents include acetone,methyl acetate, dimethylacetate, ethyl acetate, dioxane, alcohols,chloroform, methylene chloride, acetonitrile, toluene, methyl ethylketone, tetrahydrofuran, dimethylformamide, dimethylsulfoxide,cyclohexanone, acetates including butyl acetate, dimethylacetate,1-methoxy-2-propanolacetate, and so forth, and mixtures thereof. Thepolymer may usually be dissolved in the solvent by shaking or bystirring at room temperature, but if necessary, an elevated temperature,such as about 40-50° C., may be utilized to dissolve the polymer. Thecoating thickness on the balloon may be adjusted by changing theconcentration of the polymer solution. Typically, the concentration ofpolymer in solution will be about 1% to 60%, more preferably about 5% toabout 55%, and most preferably about 10% to 50%. The concentration ofthe polymer in solution to some degree depends on the particularapplication with which the medical device will be coated. Someapplications require lower viscosity solutions than others. Forinstance, spray applications may require polymer concentrations of about10% to about 20% while pad printing may require higher polymerconcentrations of about 20% to about 50%.

The solvent is then desirably evaporated from the coating, leaving onlythe polymer remaining. This may be accomplished either at ambienttemperatures, or the evaporation process by be accelerated by drying atelevated temperatures.

Thermoplastic polymers become molten and flowable when subjected toheat. However, the polymers useful to the present invention preferablyhave high tensile strength. Such high strength polymers also typicallyhave high molecular weights and would require quite high temperatures ofover 150° C. to lower the viscosity enough to apply using conventionalcoating techniques. The balloon materials, being in thin film, would besensitive to such high temperatures and it would therefore bedetrimental to apply the coating to the balloon with high temperatures.

The coating is preferably applied when the balloon is in its inflatedstate. Coverage of the coating is preferably limited to the body of theballoon, and is not found on the waist or cone portions of the balloon.A particularly preferred method of application is pad printing. The padsare typically formed from a soft silicone rubber. Such materials wouldhave less of a tendency to cause any abrasions in the balloon material.The pad picks up the image or pattern to be printed from an etchedplate, and then transfers the coating pattern to the balloon. Using thismethod, the coating may be wrapped around curved surfaces easily. Theshape and design of the pattern can be easily varied. One preferredpattern may be referred to as a “waffle” pattern in which the coatingactually resembles a waffle.

Film thickness of the coating is preferably from about 0.1 to about 3mils, more preferably from about 0.1 to 1.5 mils, and most preferablyfrom about 0.2 to 1 mil.

The coating improves the durability of the balloon by making it moreabrasion, scratch and puncture resistance. Furthermore, should anabrasion, scratch or puncture occur in the underlying balloon wall, thediscontinuous nature of the outer protective coating prevents it frominflating on its own and pulling away from the balloon wall, which inturn prevents bulging or bubbles which can cause dissection of bloodvessels or arteries. A particular problem with the formation of suchballoons is the occurrence of what is referred to in the industry as“pinholes.” Inflation medium escapes through these pinholes causing theouter coating to inflate on its own forming a bulge or bubble which cancause the dissection of a blood vessel of artery. The present inventionovercomes such problems.

EXAMPLES

The following ingredients were utilized in preparing the coatingcomposition for Example 1 and for Comparative Example A:

10% SMP-3510, polyurethane polymer available from Mitsubishi HeavyIndustries, Ltd.

70% dimethylacetate (DMAC)

15% toluene

5% tetrahydrofuran (THF)

Example 1

The coating composition shown above was brushed on a dilatation balloonin a striped pattern. This pattern was accomplished by masking offsections of the balloon and brushing on the coating so that the maskedsections had no coating. The coating was dried and the toluene, DMAC andTHF were evaporated off leaving only the polyurethane, SMP-3510 on theballoon. The balloon, which had a pinhole in its wall, was theninflated. The pinhole was in the center of a coated section of balloon.The inflation medium flowed out of the pinhole and vented out of thesides of the coated section so that no aneurysm occurred in the coating.

FIG. 5 illustrates the coated balloon in its uninflated state. Thepinhole is right of center and located beneath a coated section of theballoon. FIG. 6 illustrates the coated balloon in its inflated state. Ascan be seen from the illustration, the inflation medium is ventingaround the sides of the coating as desired. No aneurysm is formed in thecoating.

Comparative Example A

A continuous coating of the composition shown above was brushed on adilatation balloon. The coating was dried, evaporating off the toluene,DMAC and THF and leaving only the polyurethane, SMP-3510 on the balloon.The balloon had a pinhole in its wall, and upon inflation, a largebubble or aneurysm occurred in the coating as is shown in FIG. 7.

Example 2

A coating comprising a polyurethane polymer in a mixture of solventsavailable from Creative Materials under the tradename of CMI 118-43 waspad printed on a catheter balloon in a waffle pattern so as to eliminatethe possibility of pinhole formation.

1. A medical balloon insertable in the body, said medical device havinga substantially uniform noncontinuous protective surface coating, themedical balloon is formed from a first polymer layer, the first polymerlayer is exposed where the coating is noncontinuous.
 2. The dilatationballoon of claim 1 wherein the first polymer layer is a thermoplastic.3. The dilatation balloon of claim 2 wherein said coating is applied inthe form of a waffle pattern, stripe pattern or a pattern havingcircular perforations.
 4. The medical device of claim 1 wherein saidcoating is applied in a waffle pattern, stripe pattern or a patternhaving circular perforations.
 5. A dilatation balloon having improveddurability formed from a thermoplastic polymer, said balloon having anon-continuous protective coating, the balloon formed from a firstpolymer layer, wherein the first polymer layer is exposed where theprotective coating is non-continuous.
 6. The dilatation balloon of claim5 wherein said balloon is formed from a polymer selected from the groupconsisting of polyethylene terephthalate, high density polyethylene,polyamides, polyether block amides, polycarbonates, stiff polyurethanes,and mixtures thereof.
 7. The dilatation balloon of claim 5 wherein saidcoating comprises a polymeric material selected from the groupconsisting of thermoplastic polymeric and thermosetting polymericmaterials.
 8. The dilatation balloon of claim 5 wherein said coatingcomprises a polyurethane.
 9. The dilatation balloon of claim 5 whereinsaid noncontinuous coating is selected from the group consisting of awaffle pattern, a stripe pattern and a pattern having circularperforations.
 10. The dilatation balloon of claim 5 wherein said balloonis formed from a noncompliant material.
 11. A medical device insertablein the body having a protective coating on a surface thereof, saidcoating being applied to said medical device in a substantially uniformdiscontinuous pattern, the medical device formed from a first polymerlayer, the first polymer layer is exposed by the substantially uniformdiscontinuous pattern of the protective coating.
 12. The medical deviceof claim 11 wherein said coating comprises a thermoplastic polymer,thermosetting polymer or mixture thereof.
 13. The medical device ofclaim 11 wherein said medical device is a dilatation balloon.
 14. Themedical device of claim 13 wherein said coating is applied in the formof a waffle pattern, stripe pattern or a pattern having circularperforations.